Problem: $\dfrac{3}{5} - \dfrac{1}{8} = {?}$
$ = {\dfrac{3 \times 8}{5 \times 8}} - {\dfrac{1 \times 5}{8 \times 5}} $ $ = {\dfrac{24}{40}} - {\dfrac{5}{40}} $ $ = \dfrac{{24} - {5}}{40} $ $ = \dfrac{19}{40}$